The present invention relates to a biochemical process system for treating contaminated soil and liquid to remove toxic volatile organic compounds (VOCs), objectionable volatile inorganic compounds (VICs), heavy metals, and surfactants from a contaminated site. The process system of this invention removes both volatile and nonvolatile pollutants in one apparatus and represents a low cost and highly efficient alternative to present site remediation technology which is expensive and causes secondary pollutions.
The sites which are contaminated by hazardous substances are distributed throughout the entire world, occurring in various geological settings and in urban as well as rural areas. A wide range of volatile chemical wastes has been deposited at various land sites, and the extent and severity of the resulting environmental contamination is unthinkable.
The extent of site remedial action required to protect the public health and welfare is influenced by numerous factors, many of which are site specific. The types of hazardous chemicals present on-site, the potential for migration, the degree of contamination, extent of the area affected, and the costs of remedial action alternatives are all issues that must be considered. Other important issues include the relationship to drinking water sources and population centers, potential secondary pollutions, and the potential for land reuse. Costs of site remediation vary greatly, ranging from several hundred throusand U.S. dollars up to U.S. $25 million per site in 1991. In view of the large number of contaminated sites around the world and the extent of effort required to properly remediate these sites, issues related to site remediation are of international significance.
For a proper site remediation project, both contaminated soil and contaminated groundwater must be cleaned. The contamination becomes very serious if the groundwater is a drinking water source. About 70 percent of potable water in the U.S.A. is supplied by groundwater. Site contamination, which is a national major concern, is about 71 percent caused by industrial accidents (chemical spills, tank leaks, etc.), 16 percent caused by railroad or truck's chemical accidents, and 13 percent caused by leachates from lagoons or dumpsites.
The primary reason for cleaning soil is public health protection. The primary reasons for treating groundwater are: potable use (39 percent), clean-up of aquifer to prevent spread of contamination (48 percent), and industrial and commercial use (13 percent). In any case, the potentially hazardous VOCs must be removed. Timely clean-up of aquifer to prevent spread of contamination is extremely important because the damage can be beyond repair if the spread of contamination is too wide.
Toxic organic compounds commonly found in groundwater include, but are not limited to, the following:
______________________________________ Organic Compounds Percent of Concentration in Groundwater Occurrences Range ______________________________________ Carbon tetrachloride 5 130 ug/l- 10 mg/l Chloroform 7 20 ug/l- 3.4 mg/l Dibromochloropropane 1 2-5 mg/l DDE 1 1 ug/l DDE 1 1 ug/l DDT 1 4 ug/l CIS-1,2-dichloroethylene 11 5 ug/l-4 mg/l Dichloropentadiene 1 450 ug/l Diisopropyl ether 3 20-34 ug/l Tertiary methyl-butylether 1 33 ug/l Diisopropyl methyl phosphonate 1 1,250 ug/l 1,3-dichloropropene 1 10 ug/l Dichlorethyl ether 1 1.1 mg/l Dichloroisopropylether 1 0.8 mg/l Benzene 3 0.4-11 mg/l Acetone 1 10-100 ug/l Ethyl acrylate 1 200 mg/l Trichlorotrifloroethane 1 6 mg/l Methylene chloride 3 1-21 mg/l Phenol 3 63 mg/l Orthochlorophenol 1 100 mg/l Tetrachloroethylene 13 5 ug/l-70 mg/l Trichloroethylene 20 5 ug/l-16 mg/l 1,1,1-trichloroethane 8 60 ug/l- 25 mg/l Vinylidiene chloride 3 5 ug/l-4 mg/l Toluene 1 5-7 mg/l Xylenes 4 0.2-10 mg/l EDB 1 10 ug/l Others 1 NA ______________________________________
Other common contaminants in groundwater include: volatile inorganic compounds (VICs), surfactants, iron, manganese, calcium hardness, magnesium hardness, coliform bacteria, and virus.
The present technologies for soil cleaning include: surfactant washing, neutralization, solidification, incineration, chemical oxidation, bio-oxidation, lime treatment, venting, etc.
The present technologies for groundwater treatment include: air stripping tower without air emission control, non-regenerative gas phase granular activated carbon, chemical oxidation, non-regenerative liquid phase granular activated carbon, active charcoal fiber, biological processes, ion exchange, ultrafiltration, H.sub.2 O.sub.2 treatment, reverse osmosis (RO), ozonation, lime softening, ultraviolet (UV), chemical coagulation, sedimentation, filtration and chlorination. Air stripping tower without air emission control is the most common process for VOCs removal, but is not acceptable in many states. Liquid-phase granular activated carbon (GAC) contactor is technically feasible for water purification, but may be economically unfeasible when it is used alone. Chemical oxidation alone or UV alone is not cost-effective for VOCs reduction. Certain chemicals may even give undesirable residuals. Ultrafiltration and RO are excellent post-treatment process, requiring adequate pretreatment for cost reduction. Biological process is very efficient for removal of organic contaminants, but causes air pollution and requires thorough disinfection.
While conventional ozonation, UV, RO and chlorination are all effective disinfection processes, they all require separate reactors.
The present invention represents a package apparatus for removal of VOCs, VICs, heavy metals, and surfactants from contaminated soil and/or contaminated groundwater. It is an efficient and cost-effective site remediation system which considers the affordability, performance, governmental acceptance, secondary pollution elimination, mobility, simplicity in operation, and small requirement in land space.